Formerly, digitizer function-equipped liquid crystal display devices, more specifically, various types of liquid crystal display devices which can perform input operation of information by designating the position on a display screen provided therein with an input pen (pen type input device), etc., have been proposed. For these digitizer function-equipped liquid crystal display devices, liquid crystal display devices provided with a digitizer function of an electromagnetic induction type generally have, between a liquid crystal display panel and a backlight device for irradiating the liquid crystal display panel with light, an electrode wire (hereinafter, referred to as loop antenna) serving as a sensor for detecting the coordinate position of a location (point) input by operation of a pen type input device on a display screen of the liquid crystal panel. The electrode wire has a configuration in which conductive super-thin metal wires are arranged in a matrix on a sensor electrode board made of a transparent material so as to detect the coordinates in X-axis direction and Y-axis direction.
The digitizer of an electromagnetic induction type includes a pen type input device provided with a coil and a sensor electrode board in which a loop antenna for detecting the coordinates in X-axis direction and Y-axis direction is arranged. A current is applied to the coil of the pen type input device to generate a magnetic field, and the nib of the pen type input device is brought into contact with the surface of the display screen of the liquid crystal display device (liquid crystal panel). Then, a current is generated in the loop antenna by electromagnetic induction. A control device which controls operation of the digitizer can determine the coordinate position pointed with the pen type input device by analyzing information concerning a value of the generated current, position on the loop antenna at which the current is generated, and the like.
The above-mentioned liquid crystal display device with the sensor electrode board having the loop antenna arranged has the following problems formerly.
(1) Light emitted from the backlight device toward the liquid crystal panel causes wire shadow of the loop antenna by passing the sensor electrode board in which the loop antenna is arranged. This often caused a phenomenon that the wire shadow is projected on the liquid crystal panel. The projection of the wire shadow on the liquid crystal panel made an image displayed on the liquid crystal panel obscure and made it difficult for a user performing input operation of the coordinate position by using the pen type input device on the display screen to designate an accurate position.
(2) In order to solve the trouble of (1), the line width of the loop antenna sensor wire was made thin as much as possible to a level not more than 0.1 mm so as to make the wire shadow hard to occur.
As a technique to prevent the projection of the loop antenna wire shadow on the liquid crystal panel, inventions disclosed in the following Patent Documents 1 to 3 have been proposed.    [Patent Document 1] JP-A-7-104910    [Patent Document 2] JP-A-7-104935    [Patent Document 3] JP-A-2002-182197
Patent Document 1 discloses a backlight type liquid crystal display device comprised by sequentially arranging a liquid crystal panel, a light diffusion plate, and a light guide plate equipped with a light source at its side edge, and configured to prevent the wire shadow of a loop antenna from being projected on a liquid crystal panel by laying the loop antenna having the line width of 50 μm or less on the light guide plate at its liquid crystal panel display device side.
Patent Document 2 discloses a liquid crystal display device comprised by sequentially arranging a liquid crystal panel, a light diffusion plate, a light source, and a reflective plate, and configured to prevent the wire shadow of a loop antenna from being projected on a liquid crystal panel by laying and fixing the loop antenna on the plate surface of the light diffusion plate. Patent Document 2 further discloses that when a loop antenna having the line width of 50 μm or less is laid on the light diffusion plate, the wire shadow of the loop antenna is not projected on the liquid crystal panel.
Patent Document 3 discloses, with the aim of reducing the size and weight of a reflection type liquid crystal display device which does not use a backlight, a reflection type liquid crystal display device configured to prevent the wire shadow of the pattern of a loop antenna from occurring by providing, on the back of a liquid crystal panel, a sensor board in which the loop antenna used for a digitizer is arranged.